AP STATISTICS 2010 SCORING GUIDELINES Question 1 Intent of Question The primary goals of this question were to assess students ability to (1) apply terminology related to designing experiments; (2) construct an appropriate plot that could be used to investigate the fit of a linear model; (3) decide, from a graphical display, whether a linear regression model is appropriate for a set of data. Solution Part (a): i. The treatments are the different concentrations of garlic in the food granules. Specifically, there are five treatments: 0 percent, 2 percent, 10 percent, 25 percent and 50 percent. ii. The experimental units are the birds (starlings), each placed in an individual cage. iii. The response is the number of food granules consumed by the bird. Part (b): i. The following scatterplot results from these data. ii. The curved pattern in this scatterplot reveals that a linear regression model would not be appropriate for modeling the relationship between these variables. Scoring Parts (a) and (b) are scored as essentially correct (E), partially correct (P) or incorrect (I). Part (a) is scored as follows: Essentially correct (E) if the student correctly identifies all three subparts the treatments, the experimental units and the response that will be measured. Partially correct (P) if the student identifies two subparts correctly. Incorrect (I) otherwise. 2010 The College Board.
AP STATISTICS 2010 SCORING GUIDELINES Question 1 (continued) Notes In subpart ii, it is acceptable to identify the experimental units as the cages. In subpart iii, it is not correct to identify the response as the mean number of granules consumed. Part (b) is scored as follows: Essentially correct (E) if the student produces a correct graph (a reasonable scatterplot or residual plot with correct labels and scales) and then concludes, based on one or more features of the graph, that the pattern of the relationship does not appear to be linear. Partially correct (P) if the student produces a correctly shaped graph but concludes that the data are linear OR if the student produces an incorrectly shaped graph but makes a reasonable conclusion based on one or more features of the graph. Incorrect (I) if the student does not include a graph OR if the student produces an incorrect graph and does not make a reasonable conclusion based on one or more features of the graph. Note: Any of the following will result in an incorrect graph. Incorrect scale Reversed axes Missing label(s) Other types of graph (histogram, bar graph, etc.) 4 Complete Response Both parts essentially correct 3 Substantial Response 2 Developing Response One part essentially correct and one part partially correct OR One part essentially correct and one part incorrect Both parts partially correct 1 Minimal Response One part partially correct and one part incorrect 2010 The College Board.
AP STATISTICS 2010 SCORING COMMENTARY Question 1 Overview The primary goals of this question were to assess students ability to (1) apply terminology related to designing experiments; (2) construct an appropriate plot that could be used to investigate the fit of a linear model; (3) decide, from a graphical display, whether a linear regression model is appropriate for a set of data. Sample: 1A Score: 4 In part (a), subpart i, the student correctly lists the five treatments. It should be noted that the parenthetical statement (amount of galic [sic] infused in corn) could be viewed as the factor (or variable) involved in the experiment and, if given alone, would not be a correct response for this component. In part (a), subpart ii, the answer is clear and correct. In part (a), subpart iii, although the student identifies the response that will be measured as the birds adverse reaction rather than the amount eaten, it is acceptable to say that the adverse reaction is measured by the amount eaten. As all three subparts are correct, part (a) was scored as essentially correct. In part (b), subpart i, the student draws a well-labeled and correct scatterplot. In part (b), subpart ii, the response correctly states that the linear model is inappropriate because the data exhibits a more exponential pattern. This first sentence is sufficient to answer this subpart correctly. The second sentence presents a nice argument based on a change in the rate of consumption; this also would have been sufficient to correctly answer this subpart. So there are two parallel solutions to this subpart, and both are correct. As both components of part (b) are correct, it was scored as essentially correct. Both parts (a) and (b) were scored as essentially correct, so the response earned a score of 4. Sample: 1B Score: 3 In part (a), subpart i, the five concentrations of garlic oil is sufficient to correctly answer this component. In part (a), subpart ii, the response identifies the 40 birds as the experimental units, so it is correct. The statement dividing the birds into groups is extraneous. In part (a), subpart iii, the response is clear and correct. As all three subparts are correct, part (a) was scored as essentially correct. In part (b), subpart i, the student draws a residual plot but places the wrong variable along the horizontal axis, so this component was scored as incorrect. In part (b), subpart ii, the response identifies the curved shape of the residual plot and therefore correctly concludes that linear regression is not appropriate. With one of the two subparts correct, part (b) was scored as partially correct. Because part (a) was scored as essentially correct and part (b) was scored as partially correct, the response earned a score of 3. Sample: 1C Score: 2 In part (a), subpart i, the student gives a clear and detailed correct response. In part (a), subpart ii, the student identifies two experimental units, the number of food granules and garlic oil concentration. Neither of these is correct. The statement about the explanatory and response variable was considered extraneous and certainly does not improve the answer. This subpart was scored as incorrect. In part (a), subpart iii, the student correctly identifies the response that will be measured in the first sentence. The statements concerning the hypotheses were considered extraneous. As two of the three subparts are correct, part (a) was scored as partially correct. In part (b), subpart i, the student draws a bar chart, 2010 The College Board.
AP STATISTICS 2010 SCORING COMMENTARY Question 1 (continued) making this subpart incorrect. In part (b), subpart ii, the response identifies the curved ( roughly negative exponential ) shape of the data by looking at the top left corner of the bars, essentially treating these positions as points on a scatterplot. This interpretation is reasonable for the given graph, so this response was scored as correct. With one of the two subparts correct, part (b) was scored as partially correct. Because both parts (a) and (b) were scored as partially correct, the response earned a score of 2. 2010 The College Board.